This is a proposal to continue a program-project directed to the comprehensive understanding of the basic derangements of cell function which lead to mental retardation in children. The underlying approach is the application of biochemical techniques to delineate the abnormalities responsible for retardation syndromes associated with inherited metabolic diseases by investigation of model systems ranging from patients and intact animals to isolated cells and subcellular systems. Emphasis will be placed on growth and devlopment as important factors. The program project is composed of our individual research projects each to be direced by an experienced researcher. These are 1) Nitrogen metabolism in the brain and whole body: studies with gas chromatography-mass spectrometry, 2) Effects of axolemma, glial growth factor, and the ketone bodies on proliferation and differentiation of oligodendroglia and astroglia, 3) Galactose metabolism and nutritional neurotoxicity and 4)\Neuronal cells as model systems for mental dysfunction.